I’m a mechanic and fuel-related issue is amongst the most common ATV performance issues. You are in the right place for fuel pump testing and diagnosis, very shortly we’ll have this figured out.
There are five common ways to check if an ATV fuel pump is in good working order, they include:
- Listen for pump sound
- Check power at the pump
- Check pump resistance
- Visually check pump flow
- Use fuel pressure gauge to test system pressure
In this post, we’ll cover faulty ATV fuel pump symptoms. We’ll cover the range of fuel pump tests open to you, and how to execute them. We’ll also cover fuel pump replacement.
Symptoms of Faulty ATV Fuel Pump
Because some electric fuel pumps don’t fail completely, the range of symptoms can vary. The most common symptom is as you guessed a no start and in many ways, a no-start is easier to diagnose than a poor performance issue. Anyhow here is a list of the most common symptoms associated with a fuel pump issue:
- No-start
- Extended crank (hard starting) (may also be caused by pump check valve)
- Idles but won’t take rev
- Poor top-end performance
- Starts then dies
If you have one or more of these symptoms we’ll suspect a faulty pump. But before we start ordering parts we’ll need to confirm our suspicions and that’s what we’ll do next.
ATV Fuel Pump Type
Not all ATVs have a fuel pump fitted some smaller older ATVs employ gravity feed. However, if your bike has a fuel pump then it will be either mechanical or electric.
Mechanical pump – Mechanical fuel pumps are fitted to older carburetor bikes. They usually employ a pulsing engine vacuum and a diaphragm to move gas from the tank to the carburetor.
Electric fuel pump – Most modern ATVs are fuel injected and therefore require higher fuel pressure which means they are fitted with an electric fuel pump. The pump is located inside the gas tank itself.
We will diagnose both mechanical and electric pumps in this post.
How to Diagnose ATV Electric Fuel Pump
An electric pump is as you know submerged inside the gas tank and usually requires tank cover and side shrouds etc removed before we can access the pump, fuel line, or wiring terminal block connector. That’s an investment of time and energy and so we’ll run a simple listening test first to confirm we have a fuel pump issue before pulling our bike apart needlessly.
Obviously, if our pump fails this first test we’ll need to strip a few covers.
Listen for pump sound
This test is simple, but you will need a charged battery and somewhere quiet to perform the test. Most electric fuel pumps emit an audible buzz or hum sound for about 3 seconds when the ignition is turned on initially. The pump does this so as to pressurize the fuel line and prime the fuel injector in preparation for starting.
The first test is simple then, turn the ignition switch on (position 2) and listen.
Two results are possible:
1 You hear a humming sound – Hearing the fuel pump hum, is a good sign, it means the wiring circuit and ECU are all doing their job, it also means the pump is working. and if you are chasing a no-start problem, the fuel pump likely isn’t the root cause.
But a hum from the pump doesn’t necessarily mean the pump is working as it should. The pump may not be supplying enough flow and that’s a common cause of symptoms such as extended crank or poor performance. If that is the type of problem you are chasing, we’ll need to remove some covers and access the pump for some testing.
2 You don’t hear a humming sound – There may be a few reasons you don’t hear the pump. The most common reasons are: the pump may indeed be faulty or the fuel pump fuse may be blown.
Since checking the fuse is a ton easier than pulling covers etc and checking the pump, we’ll check the fuse first.
Fuses commonly blow because:
- Amp rating too small
- Circuit short
- Faulty fuel pump
Some ATV fuses are located under the seat but you may need to consult your manual for fuel pump fuse location and fuse amp rating.
Check power at the pump
Ok, you already know you’ll need to strip out covers, etc to gain access to the pump terminal block connector. When you have gained access we’ll need a DVOM or test light to check for voltage. If you need tools for the job, check out the tools I use here on the ATV tools page.
The process is as follows:
- Locate and disconnect pump block connector
- Probe power and ground terminals (careful not to damage the terminals)
The power will only be present for 3 sec after ignition in position 2
Two results are possible:
1 You have power at the terminal, if so jump ahead to the resistance test here.
2 No power at the pump terminal, check power and ground independently using a test light.
Test power at the pump using the battery ground as per the picture.
The power will only be present for 3 sec after ignition in position 2
Test ground at the pump using the battery positive as per the picture.
The power will only be present for 3 sec after ignition in position 2
If you are missing either power or ground suspect a wiring break and chase them.
Check pump resistance
A resistance test is useful as it allows us to ascertain the pump circuit without having to remove it from the tank. When running a resistance test you must isolate the component from the circuit.
When testing resistance the meter sends a small charge down one side of the circuit and the second probe measures its progress.
Test as follows:
Set the DVOM to resistance Ω and probe both sides of the pump terminals.
Two results are possible:
Meter offers a resistance reading – A reading in the region of 6 ohms is typical but all bikes will have their own window of operation. You’ll need to check your reading is within it.
Meter offers an open reading – An open means the pump has an open circuit and is faulty. Pumps can’t be repaired, they are replaced. And we cover that below.
Visually check pump flow
For this test, we’ll need an empty water bottle, length of fuel line, and an appropriate small pick to remove the fuel line from the fuel pump. The pump wiring will need to be connected.
The process is as follows:
- Remove the fuel line from the pump
- Fit length of fuel line to fuel pump and feed into a water bottle
- Activate the pump (ignition switch position 2)
No fuel flow or a weak flow means the pump needs to be replaced.
A solid flow means it appears the pump is good, that said manufacturers do have a min quantity flow over a given time.
Use fuel pressure gauge to test system pressure
For this test, we’ll need a fuel pressure test kit. Your manufacturer will specify a min fuel pressure and head pressure specs for the pump.
I look for the pressure to be maintained with key on and then when running check the min spec is being maintained when the engine is loaded. Somewhere between 40 to 60 psi is typical.
The process is as follows:
- Connect fuel pressure gauge
- First check key on fuel pressure.
- Now check min pressure with the engine running.
If the pump fails this test, go ahead and replace it.
How To Change ATV Electric Fuel Pump
To fit a fuel pump we’ll need mostly regular hand tools but some models may require a special fuel pump release tool, but a good set of channel locks does the job too.
The process is as follows:
- Remove fuel line
- Remove pump wiring terminal
- Clean the area around the pump
- Mark the location of the keeper (lets you know how much to tighten later)
- Using channel locks loosen and remove the keeper
- Remove pump and sender unit
The pump and sender unit are usually removed as one unit, meaning we’ll need to remove the pump from the assembly.
The process is as follows:
- Move to a workbench and remove the filter mesh from the pump
- Remove the pump push-on wire terminals (take a pic first if needed)
- Remove fuel line
- Remove pump from sending unit
Refitting is the reverse. However, some new pump kits may include pump O-ring seals and fuel line length and clips. It depends on the pump type fitted.
Pump fitting tips:
- Use non-petroleum lube on rubber seals to help fitting and sealing (silicone grease)
- Use dielectric grease on electrical terminals helps prevent moisture
- Tighten pump keeper to your mark
- Check for leaks after rebuild
How to Diagnose ATV Mechanical Fuel Pump
The mechanical fuel pump is a lot easier to locate, test, and work on. The pump is usually small and located close to the gas tank. Following the fuel line from the gas tank will help you locate the pump.
It will employ a fuel line in (from the gas tank) and a fuel line out (to the carburetor) and a pulsing hose that’s connected to the engine crankcase breather system.
Some checks we can run before removing any components include:
- Check that we have sufficient fuel inside the gas tank
- Check the gas tap is turned fully on
- Check the vacuum hose to the pump (a split, perished or otherwise damaged hose will prevent the pulsing vacuum needed to power the pumping action)
With these simple checks out of the way, we can now begin to diagnose. The steps are as follows:
- Remove the carburetor fuel line and place the open end into a suitable clear container (an empty water bottle works great)
- Have helper crank over the motor
- Check fuel flow to the container
A good pump will pulse a plenty feed of fuel
A bad pump will supply no fuel or poor fuel flow
Replacing a mechanical is an easy task requiring only basic tools. But do check that vacuum line, it is critical to fuel pump operation. Replace fuel line clamps and check for leaks on completion.
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John Cunningham is a technical writer here at ATVfixed.com. He’s a Red Seal Qualified Service Technician with over twenty-five years experience. He’s worked on all types of mechanical equipment, from cars and trucks to ATVs and Dirt bikes.